The task is to match five transmission lines connected together. Some practical results have been reported using various ring and star schemes in microstrip and stripline media for frequencies up to 18 GHz. (See: E. R. Hansen and G. P. Riblet, "An Ideal Six-Port Network Consisting of Matched Reciprocal Five-Port and a Perfect Directional Coupler", IEEE Trans. Microwave Theory Tech., Vol. MTT-31, No. 3, pp. 284-288, March 1983, and M. Malkomes et al., "Optimized Microstrip Ring-Star Five-Ports for Broadband Six-Port Measurement Applications", in 1984 IEEE MTT-S Digest, pp. 472-474, May 1984). These matching technqiues employ standard matching sections using Computer Aided Design and are, therefore, restricted to TEM transmission media and low frequencies where CAD is available. A five-port waveguide junction suitable for millimeter wavelengths was not available in the prior art.